Can anyone help me find this study that Ray references?

[EnergeticLeo]

Ray talks about a group of women trying to lose weight who were found to be able to gain weight on even 700 calories a day, where the food was controlled in metabolic wards. He mentions it here, for example:

View: https://youtu.be/yylOTFJFxko?t=1203


Does anyone know what study he's referring to? I've searched without any success.